The present invention relates generally to welding systems and, more particularly, to a welding machine designed to introduce a consumable wire electrode to a weld and having an inverter to condition a 115 volt raw power input to a form usable by the welding process.
MIG welding, formerly known as Gas Metal Arc Welding (GMAW), combines the techniques and advantages of TIG welding's inert gas shielding with a continuous, consumable wire electrode. An electrical arc is created between the continuous, consumable wire electrode and a workpiece. As such, the consumable wire functions as the electrode in the weld circuit as well as the source of filler metal. MIG welding is a relatively simple process that allows an operator to concentrate on arc control. MIG welding may be used to weld most commercial metals and alloys including steel, aluminum, and stainless steel. Moreover, the travel speed and the deposition rates in MIG welding may be much higher than those typically associated with either Gas Tungsten Arc Welding (TIG) or Shielded Metal Arc Welding (stick) thereby making MIG welding a more efficient welding process. Additionally, by continuously feeding the consumable wire to the weld, electrode changing is minimized and as such, weld effects caused by interruptions in the welding process are reduced. The MIG welding process also produces very little or no slag, the arc and weld pool are clearly visible during welding, and post-weld clean-up is typically minimized. Another advantage of MIG welding is that it can be done in most positions which can be an asset for manufacturing and repair work where vertical or overhead welding may be required.
To ease portability, MIG welding systems have been designed such that the wire feeder and power supply circuitry are integrated within a single housing. Further, MIG systems have been designed to be operable on a 115 VAC input. As a result, these MIG systems may be transported to multiple welding sites and plugged into a standard and commonly available 115 volt terminal for power rather than a less common 230 volt terminal. Designing the MIG machine to be operable on a 115 volt line and integrating the wire feeder and power source in a common housing provides a relatively compact and portable unit. Generally, however, the output welding current of these portable machines must be limited so that line current does not exceed the capacity of the circuit breaker protecting the 115 VAC line. The circuit breaker is typically a 15 or 20 amp circuit breaker.
A prior art MIG welding machine operable on a 115 volt input is schematically shown in FIG. 1. A typical 115 VAC MIG machine 2 consists of a line frequency transformer 3 designed to receive an 115 VAC input 4 and feed the input to either a controlled or uncontrolled rectifier 5. The rectifier in turn feeds an output capacitor 6 and output filter choke 7. The capacitor 6 and filter choke 7 determine the welding characteristics of the MIG machine. The capacitor 6 provides an instantaneous source of stored energy which assists in the welding process by providing the high currents typically required. The output filter choke 7 limits the rate of rise of the output current which controls the harshness of the arc as well as the spatter level. That is, capacitor 6 and filter choke 7 regulate operation of wire feeder 8 to control the output 9 provided to a weld.
MIG welders having 115 VAC transformer-rectifier combination provide a relatively compact and relatively portable machine. However, these known MIG welders typically weigh 50 to 60 pounds, or more. In addition, these known MIG welders typically have a wide profile to accommodate fitting of the transformer and wire feeder in the single housing. These features detract from the portability of the welder. Also, as mentioned above, the output rating must be limited so as not to trip the input line circuit breaker. The output capacitor has a beneficial effect of being able to supply large instantaneous currents to the output, but tends to make the line draw higher because of the poor form factor of the line current. As a result, the welder has a relatively poor power factor. In addition the overall power efficiency of the transformer rectifier circuit is fairly low. For example, for a given KVA input drawn from the AC line, only about 60–65 percent is converted to usable output welding power.
It is therefore desirable to design a portable welder to carry out a MIG welding process having a 115 volt inverter to condition a raw power input with improved power factor characteristics and improved portability.